Engine Controls Self-Diagnostics: Overview Pontiac Aztek I

Description

The Diagnostic System Check is an organized approach to identifying a condition that is created by a malfunction in the powertrain control system. The Diagnostic System Check must be the starting point for any driveability concern. The Diagnostic System Check directs the service technician to the next logical step in order to diagnose the concern. Understanding and correctly using the diagnostic table reduces diagnostic time, and prevents the replacement of good parts.

Test Description

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - Lack of communication may be caused by a partial or a total malfunction of the Class 2 serial data circuit. The specified procedure determines the particular condition.
2. 5 - This step stores the Powertrain Control Module (PCM) Diagnostic Trouble Code (DTC) information into the scan tool's memory. After you complete the diagnostic procedure, review the captured information in order to catch the next DTC if the control module stores multiple DTCs. Review the Freeze Frame data and the Failure Records data. Use this information in order to determine how frequently and how recently the DTC set. This information may help diagnose an intermittent condition. Information about the operating conditions at the time that the DTC set may also help diagnose an intermittent condition. Capturing the stored information saves the data that the PCM loses during the following conditions: When a diagnostic procedures instructs you to clear the DTCs. When a diagnostic procedure instructs you to disconnect the PCM connectors. When a diagnostic procedure instructs you to replace the PCM. See «REMOVAL & INSTALLATION - AZTEC & RENDEZVOUS»(ref-155806) article.
3. 6 - The presence of DTCs which begin with "U", indicate that some other module is not communicating. Following the specified procedure will gather all the available information before you perform the tests.
4. 8 - If there are other modules with DTCs set, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155075-S27919636112003060600000). The DTC list directs you to the appropriate diagnostic procedure. If the control module stores multiple powertrain DTCs, diagnose the DTCs in the following order: Component level DTCs, such as sensor DTCs, solenoid DTCs, and relay DTCs. Diagnose the multiple DTCs within this category in numerical order. Begin with the lowest numbered DTC, unless the diagnostic table directs you otherwise. System level DTCs, for example, misfire DTCs, fuel trim DTCs, and catalyst DTCs.
5. 10 - This step is for areas that have inspection and maintenance testing procedures for emissions testing. Use this step if the testing facility found one or more I/M system status that did not set.

Several States require that a vehicle pass On-Board Diagnostic (OBD) system tests and the I/M emission inspection in order to renew vehicle registration. This is accomplished by viewing the I/M System Status display on a scan tool. Using a scan tool, the technician can observe the I/M System Status in order to verify that the vehicle meets the criteria that complies with the local area requirements.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 - Any DTCs set, even those that are not listed in the INSPECTION/MAINTENANCE SYSTEM DTCS table, may prevent the required DTCs from running. If there is any question as to whether a set DTC is disabling the required I/M diagnostic, review the Conditions for Running in the diagnostic procedures for the DTC required by the I/M diagnostic. A list of disabling DTCs, if applicable, is contained in the supporting text for that DTC.
2. 2 - Anytime a control module is reprogrammed or the diagnostic trouble codes are cleared as part of a repair procedure, all the I/M System Status indicators will reset to NO.
3. 3 - Use discretion when determining whether the entire system set procedure needs to be performed. For example, if the only tests that have not run are those that require the engine to be at operating temperature, then only those individual tests need to be run. There is no need to allow the engine to completely cool in order to run these tests.

The purpose of the I/M Complete System Set Procedure is to satisfy the enable criteria necessary to execute all of the I/M readiness diagnostics, and complete the trips for those particular diagnostics. When all diagnostic tests are complete, the I/M System Status indicators are set to YES. Perform this test when more than one or all of the I/M System Status indicators are set to NO.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 - Make sure that you perform the Inspection/Maintenance System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - This step runs the HO2S Heater Tests and initiates the EVAP System Test. Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria. The engine control module considers the engine to be cold if the following conditions are met: Engine Coolant Temperature (ECT) less than 86°F (30°C). ECT and Intake Air Temperature (IAT) are within 7°F (5°C) of each other at start-up.
3. 3 - This step runs the EVAP, AIR and the Oxygen Sensor Tests. The EVAP Test begins once the engine coolant reaches a calibrated temperature. The AIR Test, if equipped, begins shortly after Closed Loop and the indicated speed is achieved. The Oxygen Sensor Tests begin once the engine is at operating temperature, in Closed Loop fuel control, and a calibrated amount of time has elapsed.
4. 4 - This step runs the Exhaust Gas Recirculation (EGR) Tests. The EGR Tests are run during a gradual deceleration with a closed throttle. The vehicle speed is required in order to maintain a high, steady MAP signal.
5. 5 - This step runs the Catalyst Tests. This test runs during the idle period immediately following a cruise period that meets a minimum calibrated RPM and time period.
6. 6 - Perform the individual system test for any of the systems that do not update to YES.
7. 7 - The I/M System Status only reports on whether or not a diagnostic has run, not the outcome of the test. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

The purpose of this test is to satisfy the enable criteria necessary to execute Inspection/Maintenance readiness diagnostics for the catalyst system. The test may be used to set the I/M System Status indicators to YES. Ensure that the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers in procedure.

1. 1 - Make sure that you perform the Inspection/Maintenance System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - The Catalyst Test during the idle period immediately following the cruise period.
3. 3 - This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. See «DIAGNOSTIC AIDS»(ref-155075-S38476053022003060600000).
4. 4 - This step helps identify any unique or unusual criteria required to run the diagnostic test if the universal set procedure does not. This information is located in Conditions for Running DTC.
5. 5 - The I/M System Status only reports on whether or not a diagnostic has run, not the outcome of the test. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Exhaust Gas Recirculation (EGR) System. The test may be used to set the I/M System Status indicators to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 - Make sure you perform the Inspection/Maintenance System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - The EGR Active Tests are run during a gradual deceleration with a closed throttle. The vehicle speed is required in order to maintain a high, steady MAP signal.
3. 3 - This step is to identify a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. See «DIAGNOSTIC AIDS»(ref-155075-S08774739892003060600000).
4. 4 - This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in Conditions for Running DTC.
5. 5 - The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any Emission Related DTC sets after the tests are complete, the DTC will require diagnosis.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Evaporative (EVAP) emission system. The test may be used to set the I/M System Status indicators to YES. Service Bay Tests are included on the scan tool for some systems depending upon vehicle make and model. The test is designed to allow the EVAP Diagnostic Tests to run in service bay conditions. Ensure that the vehicle meets the requirements listed in Conditions for Running before performing either EVAP System Test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers in procedure.

1. 1 - Make sure that you perform the Inspection/Maintenance System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 3 - This step determines whether or not the EVAP System Test has passed. If the system is operating correctly, the scan tool indicates that the system has passed and the I/M System Status updates to YES. If the EVAP Service Bay Test aborts because of lost enable conditions, the test can be repeated once the enable criteria is met.
3. 4 - A failed DTC during the EVAP Service Bay Test may not appear in the DTC Information display on some vehicles. The Service Bay Test displays an indication of which test failed as a directive to the appropriate service information. Some vehicles will display the test as aborted and the first failure of type "B" DTC appears in the DTC Information.
4. 5 - The EVAP System Test usually begins around an engine coolant temperature of 176°F (80°C). The vehicle should be operated moderately until this temperature is reached. The engine coolant temperature can be monitored using the scan tool.
5. 6 - This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. See «DIAGNOSTIC AIDS»(ref-155075-S26205426732003060600000).
6. 7 - This step helps identify any unique or unusual criteria required to run the diagnostic test if the universal set procedure does not. This information is located in Conditions for Running DTC.
7. 8 - The I/M System Status only reports on whether or not a diagnostic has run, not the outcome of the test. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Oxygen Sensor (O2S, HO2S) system. The test may be used to set the I/M System Status to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers on the procedures.

1. 1 - Make sure that you perform the Inspection/Maintenance System Check before performing this test. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(ref-155075-S40077356142003060600000). Failure to do so may result in difficulty updating the status to YES.
2. 2 - The oxygen sensor tests begin shortly after the indicated speed is achieved. The engine RPM may be too low in overdrive on manual transmission vehicles. If difficulty is encountered updating the status, operate the vehicle in the recommended gear during the test.
3. 3 - This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. See «DIAGNOSTIC AIDS»(ref-155075-S17059128752003060600000).
4. 4 - This step helps identify any unique or unusual criteria required to run the diagnostic test if the universal set procedure does not. This information is located in Conditions for Running DTC. See «CONDITIONS FOR RUNNING»(ref-155075-S30667421882003060600000).
5. 5 - The I/M System Status only reports on whether or not a diagnostic has run, not the outcome of the test. If any Emission Related DTC sets after the tests are complete, the DTC will require diagnosis.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Heated Oxygen Sensor (HO2S) system. The test may be used to set the I/M System Status to YES. Ensure that the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers on the procedures.

1. 1 - Make sure that you perform the Inspection/Maintenance System Check before performing this test. See «INSPECTION/MAINTENANCE SYSTEM CHECK»(ref-155075-S40077356142003060600000). Failure to do so may result in difficulty updating the status to YES.
2. 2 - Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria.
3. 3 - This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. See «DIAGNOSTIC AIDS»(ref-155075-S25899336842003060600000).
4. 4 - This step helps identify any unique or unusual criteria required to run the diagnostic test if the universal set procedure does not. This information is located in Conditions for Running DTC. See «CONDITIONS FOR RUNNING»(ref-155075-S25546129702003060600000).
5. 5 - The I/M System Status only reports on whether or not a diagnostic has run, not the outcome of the test. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The PCM controls the HO2S 1 heater low control circuit with a low side driver. The HO2S 1 heater diagnostic monitors the current draw through the HO2S 1 low side driver when the engine is running. This DTC will set if the current level exceeds a calibrated amount.

Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 4 - A DTC fail in this step verifies the problem is present with the HO2S 1 disconnected.

The Mass Airflow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has an ignition 1 voltage circuit, a ground circuit, and a signal circuit. The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage in order to produce a frequency based on inlet air flow through the sensor bore. The frequency varies within a range of around 2,000 Hertz at idle to about 10,000 Hertz at maximum engine load. The PCM uses the following sensor inputs in order to calculate a predicted MAF value

1. Barometric (BARO) pressure at key ON.
2. Manifold Absolute Pressure (MAP).
3. Intake Air Temperature (IAT).
4. Engine Coolant Temperature (ECT).
5. Throttle Position (TP).
6. Engine speed (RPM).

The PCM compares the actual MAF sensor frequency signal to the predicted MAF value. This comparison will determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. DTC P0101 sets if the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 5 - This step will determine if the MAP sensor pressure is within the proper range for a given altitude.
2. 6 - This step will determine if the MAP sensor voltage is within the proper range at idle.
3. 7 - This step will determine if the MAP sensor responds properly to the change in manifold pressure.
4. 8 - This step will determine if the Throttle Position (TP) sensor is operating properly.
5. 9 - This step will determine if any mechanical faults have caused this DTC to set.

The Mass Airflow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has an ignition 1 voltage circuit, a ground circuit, and a signal circuit. The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage in order to produce a frequency based on inlet air flow through the sensor bore. The frequency varies within a range of around 2,000 Hertz at idle to about 10,000 Hertz at maximum engine load. DTC P0102 sets if the PCM detects a frequency signal lower than the possible range of a properly operating MAF sensor.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 5 - This step will determine if any mechanical faults have caused this DTC to set.
2. 7 - This voltage drop test will determine if high resistance has caused this DTC to set.
3. 9 - This step verifies the voltage signal from the PCM to the MAF sensor connector.
4. 10 - This step tests the signal circuit of the MAF sensor for a short to another 5-volt reference circuit.
5. 13 - This step will determine which portion of the circuit or which component is shorted to ground.
6. 16 - This step verifies that the signal circuit is not shorted to any other PCM circuit.

The Mass Airflow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor frequency signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has an ignition 1 voltage circuit, a ground circuit, and a signal circuit. The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage in order to produce a frequency based on inlet air flow through the sensor bore. The frequency varies within a range of around 2000 Hertz at idle to about 10,000 Hertz at maximum engine load. DTC P0103 sets if the PCM detects a frequency signal higher than the possible range of a properly operating MAF sensor.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 - This step tests for electromagnetic interference (EMI) on the signal circuit of the MAF sensor. A frequency reading with the MAF sensor disconnected indicates an EMI related fault or a poor connection. Disconnecting the MAF sensor may set additional related DTCs.
2. 4 - This step will determine if incorrect harness routing has caused this DTC to set.
3. 5 - This step will determine if water intrusion has caused this DTC to set.

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at a Wide-Open Throttle (WOT). The MAP sensor is also used in order to determine the Barometric (BARO) pressure. This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 4 - Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records can aid in locating an intermittent condition.
2. 5 - This step determines if voltage is available to the sensor. It also determines if there is sufficient current flow in the circuit.

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at a Wide-Open Throttle (WOT). The MAP sensor is also used in order to determine the Barometric (BARO) pressure. This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set.

The number below refers to the step number in the diagnostic procedures.

1. 3 - This steps tests for improper Throttle Position (TP) sensor operation.
2. 5 - If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an excessively low IAT signal voltage, indicating a high temperature, DTC P0112 sets.

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an excessively high IAT signal voltage, indicating a low temperature, DTC P0113 sets.

The number below refer to the step number in the diagnostic procedures.

1. 6 - This step tests for the proper operation of the circuit in the low voltage range.

The Engine Coolant Temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the signal circuit. When coolant temperatures are low, resistance is high. When coolant temperatures are high, the resistance is low. The PCM uses this input for engine controls and enabling criteria for diagnostics. The PCM will record the amount of time the engine is OFF. At restart, the PCM will compare the temperature difference between the ECT and Intake Air Temperature (IAT). If the temperature difference is not within the calculated amount after the predetermined soak time, this DTC will set. Before failing this test, the PCM will check for the presence of a block heater.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 7 - A snapshot is the quickest method to capture the data before it changes.
2. 8 - An IAT sensor that is skewed low can cause this DTC to set.
3. 10 - This step will determine if high resistance has caused this DTC to set.
4. 12 - A high resistance short from the signal circuit to the low reference circuit can cause this DTC to set.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, this Diagnostic Trouble Code (DTC) will set.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The ECT sensor has a signal circuit and a low reference circuit. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with the following circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide-Open Throttle (WOT) position provides the PCM with a signal voltage from less than 1 volt to more than 4 volts through the TP sensor signal circuit. When the conditions for running this DTC are met, the PCM will use the MAP sensor in order to determine if the predicted operating range of the TP sensor is correct. A skewed Manifold Absolute Pressure (MAP) sensor may cause this DTC to set. The MAP sensor should be tested for proper operation if the TP sensor is operating properly and this DTC continues to set.

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) in order to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide-Open Throttle (WOT) position provides the PCM with a signal voltage from less than one volt to more than 4 volts through the TP sensor signal circuit. If the PCM detects an excessively low signal voltage, this DTC will set.

The number below refers to the step number in the diagnostic procedure.

1. 5 - This step determines if the 5 volts supplied by the PCM is available to the sensor. It also determines if the circuit is capable of carrying the necessary amperage.

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide-Open Throttle (WOT) position provides the PCM with a signal voltage from less than one volt to more than 4 volts through the TP sensor signal circuit. If the PCM detects an excessively high signal voltage, this DTC will set.

The number below refers to the step number on the diagnostic procedures.

1. 6 - This step allows the sensor to operate and permits access to the low reference circuit for the voltage drop measurement.

An Engine Coolant Temperature (ECT) sensor monitors the coolant temperature. The Powertrain Control Module (PCM) uses this input for engine control, and for an enabling criteria for some diagnostics. The air flow coming into the engine is accumulated. The air flow is used in order to determine if the engine has been driven within conditions that would allow the engine coolant to heat normally to the thermostat-regulating temperature. If the coolant temperature does not increase normally, or if the coolant temperature does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria may not run when expected. This Diagnostic Trouble Code (DTC) will only run once per ignition cycle, within the enabling conditions. This DTC will set when there has been excessive time to reach Closed Loop fuel control.

An Engine Coolant Temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the Powertrain Control Module (PCM) for engine control and as an enabling criteria for some diagnostics. The air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected. This Diagnostic Trouble Code (DTC) will only run once per ignition cycle within the enabling conditions. If the engine coolant fails to reach a preset target temperature before a calculated air flow is accumulated, DTC P0128 will set.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. This DTC will set if the PCM receives an active HO2S 1 signal of a lower than calibrated minimum amplitude. Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. This DTC will set if the HO2S 1 voltage remains below a calibrated amount for an excessive amount of time. Each HO2S 1 has the following circuits

1. HO2S 1 high signal
2. HO2S 1 low reference
3. HO2S 1 heater ignition voltage
4. HO2S 1 heater low control
5. Low reference loop

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. This DTC will set if the HO2S 1 voltage remains above a calibrated amount for an excessive amount of time. Each HO2S 1 has the following circuits

1. HO2S 1 high signal
2. HO2S 1 low reference
3. HO2S 1 heater ignition voltage
4. HO2S 1 heater low control
5. Low reference loop

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. This DTC will set if the HO2S 1 voltage average response time is too slow. Each HO2S 1 has the following circuits

1. HO2S 1 high signal
2. HO2S 1 low reference
3. HO2S 1 heater ignition voltage
4. HO2S 1 heater low control
5. Low reference loop

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. This DTC will set if the HO2S 1 voltage remains at or near the bias voltage amount. Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The PCM controls the HO2S 1 heater low control circuit with a low side driver. The HO2S 1 heater diagnostic monitors the current draw through the HO2S 1 low side driver when the engine is running. This DTC will set if the current level is not within the calibrated range. Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The HO2S 2 is used for post catalyst monitoring. This DTC will set if the HO2S 2 voltage remains below a calibrated amount for an excessive amount of time. The HO2S 2 has the following circuits

1. HO2S 2 high signal.
2. HO2S 2 low signal.
3. HO2S 2 heater ignition voltage.
4. HO2S 2 heater ground.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The HO2S 2 is used for post catalyst monitoring. This DTC will set if the HO2S 2 voltage remains above a calibrated amount for an excessive amount of time. The HO2S 2 has the following circuits

1. HO2S 2 high signal.
2. HO2S 2 low signal.
3. HO2S 2 heater ignition voltage.
4. HO2S 2 heater ground.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The HO2S 2 is used for post catalyst monitoring. This DTC will set if the HO2S 1 voltage remains at or near the bias voltage amount. The HO2S 2 has the following circuits

1. HO2S 2 high signal.
2. HO2S 2 low signal.
3. HO2S 2 heater ignition voltage.
4. HO2S 2 heater ground.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The HO2S 2 heater performance diagnostic will only run from a cold start and only once per key cycle. This DTC will set if the HO2S 2 heater takes too long to heat based on the HO2S 2 signal voltage input to the PCM. The HO2S 2 heater circuit is energized anytime the ignition key is in the ON position. The HO2S 2 has the following circuits

1. HO2S 2 high signal.
2. HO2S 2 low signal.
3. HO2S 2 heater ignition voltage.
4. HO2S 2 heater ground.

The Powertrain Control Module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop, the oxygen sensor inputs are added and used by the PCM to calculate short and long term fuel trim (fuel delivery adjustments). If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. Short term fuel trim values change rapidly in response to the Heated Oxygen Sensor (HO2S) voltage signals. Long term fuel trim makes coarse adjustments in order to maintain air/fuel ratio of 14.7:1. If the PCM detects an excessively lean condition, this DTC will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 5 - If conditions were not corrected, see «FUEL SYSTEMS»(ref-152619-S32565021802003021700000) in BASIC DIAGNOSTIC PROCEDURES - 3.4L AZTEK & RENDEZVOUS article.
2. 6 - If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failures may be at fault.

The Powertrain Control Module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop, the oxygen sensor inputs are added and used by the PCM to calculate short and long term fuel trim, fuel delivery adjustments. If the oxygen sensors indicate a lean condition, fuel trim values will be more than zero percent. If the oxygen sensors indicate a rich condition, fuel trim values will be less than zero percent. Short term fuel trim values change rapidly in response to the Heated Oxygen Sensor (HO2S) voltage signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the Evaporative (EVAP) emission canister is causing a rich condition. If the PCM detects an excessively rich condition, this DTC will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 5 - If conditions were not corrected, see «FUEL SYSTEMS»(ref-152619-S32565021802003021700000) in BASIC DIAGNOSTIC PROCEDURES - 3.4L AZTEK & RENDEZVOUS article.
2. 6 - An EVAP canister that is saturated will cause a rich condition. Fuel in the vacuum line to the fuel pressure regulator indicates a bad regulator. If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be at fault.

The Powertrain Control Module (PCM) enables the appropriate fuel injector on the intake stroke for each cylinder. A voltage is supplied directly to the fuel injectors. The PCM controls each fuel injector by grounding the control circuit via a solid state device called a driver. The PCM monitors the status of each driver. If the PCM detects an incorrect voltage for the commanded state of the driver, a fuel injector control DTC sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - The misfire current counters may not increment if certain DTCs are set. Use a scan tool to clear the DTCs. Monitoring the misfire current counters isolates which fuel injector is not operating. A cylinder that is misfiring can also cause the misfire current counters to increment for another cylinder. Diagnose the cylinder with the highest level of misfire first.
2. 4 - This step isolates the condition. If the test light blinks, the PCM is providing ground to the fuel injector. On some vehicles the Camshaft Position (CMP) sensor must provide a signal to the PCM before the PCM will provide a ground to the fuel injector. For this reason, the CMP circuits between the fuel injector harness multi-way connectors must be jumpered.
3. 5 - This step tests if a ground is constantly being applied to the fuel injector.
4. 6 - This step isolates the circuit between the multi-way connector and the PCM. An open or short to voltage on the fuel injector control circuit will not allow the test light to blink.
5. 8 - This step inspects for fuel injector harness damage between the multi-way connector and the upper intake manifold. Careful inspection may isolate the condition before removal of the upper intake manifold.
6. 10 - Perform the continuity test at the multi-way connector. If the DVOM displays OL, test the circuits for an open or a poor connection.
7. 13 - This step isolates the circuit between the multi-way connector and the fuel injector. A short to voltage on the fuel injector control circuit will set this DTC.

The Powertrain Control Module (PCM) provides ignition positive voltage to the coil side of the fuel pump relay. When the ignition switch is first turned ON, the PCM energizes the fuel pump relay, which applies power to the fuel pump. The PCM enables the fuel pump relay as long as the engine is cranking or running, and crankshaft reference pulses are received. If no crankshaft reference pulses are received, the PCM de-energizes the fuel pump relay after 2 seconds. The PCM monitors the voltage on the fuel pump relay control circuit. If the PCM detects an incorrect voltage on the fuel pump relay control circuit, DTC P0230 sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - Listen for a click when the fuel pump relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 4 - This step verifies that the PCM is providing voltage to the fuel pump relay.
3. 5 - This step tests for an open in the ground circuit to the fuel pump relay.
4. 6 - This step determines if voltage is constantly being applied to the control circuit of the fuel pump relay.

The Powertrain Control Module (PCM) uses information from the Crankshaft Position (CKP) sensor and the Camshaft Position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause three-way catalytic converter damage. The Malfunction Indicator Light (MIL) will flash ON and OFF when the conditions for catalytic converter damage are present.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - If actual CKP variation values are not within the learned values, the misfire counters may increment.

The Knock Sensor (KS) produces an alternating current voltage at all engine speeds and loads. The Powertrain Control Module (PCM) then adjusts the spark timing based on the amplitude and on the frequency of the KS signal. The PCM uses the KS signal in order to calculate the average voltage and assigns a voltage value. The PCM checks the KS and the related wiring by comparing the actual knock signal to the assigned voltage range. A normal KS signal should remain out of the assigned voltage range. This DTC will set if the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system.

The Knock Sensor (KS) produces an alternating current voltage at all engine speeds and loads. The Powertrain Control Module (PCM) adjusts spark timing based on the amplitude and on the frequency of the KS signal. The PCM uses the KS signal in order to calculate the average voltage and assigns a voltage value. The PCM checks the KS and the related wiring by comparing the actual knock signal to the assigned voltage range. A normal KS signal should stay outside the assigned voltage range. This DTC will set if the KS signal is within the assigned voltage range or if the KS signal is not present.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 - A fault in the 12-volt reference circuit of the 24X CKP sensor or the CMP sensor can cause this DTC to set.
2. 6 - Tapping on the engine block will simulate an engine knock.

The circuit uses 2 different types of Crankshaft Position (CKP) sensors. The CKP sensor "B" is connected directly to the Ignition Control (IC) module, and consists of the following circuits

1. CKP sensor 1 signal circuit.
2. Low reference circuit.

The CKP sensor "A" connects directly to the PCM module, and consists of the following circuits

1. The 12-volt reference circuit.
2. Medium resolution engine speed signal circuit.
3. Low reference circuit.

If the PCM detects an incorrect number of CKP pulses, DTC P0336 sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 4 - If sent here from DTC P0327 proceed with DTC P0336 diagnostic even if P0336 has not failed this ignition.
2. 8 - The 24X RPM on the scan tool should change each time the Medium Resolution Engine Speed Signal circuit is touched.

During cranking, the Ignition Control (IC) module monitors the 7X Crankshaft Position (CKP) sensor signal. Once the engine starts, the IC module determines spark synchronization by the Camshaft Position (CMP) sensor pulses. The Powertrain Control Module (PCM) constantly monitors the number of pulses on the CMP signal circuit and compares the number of CMP pulses to the number of 24X reference pulses and the number of 3X reference pulses being received. If the PCM receives an incorrect number of pulses on the CMP signal circuit, DTC P0341 will set.

The Powertrain Control Module (PCM) tests the Exhaust Gas Recirculation (EGR) system during deceleration by momentarily commanding the EGR valve to open while monitoring the Manifold Absolute Pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should see a proportional increase in MAP. If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set this DTC. The number of test samples required to accomplish this may vary according to the amount of detected flow error. Normally, the PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows twelve test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between nine and twelve samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test.

The number below refers to the step number in the diagnostic procedure.

1. 2 - MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.

The Powertrain Control Module (PCM) monitors the Exhaust Gas Recirculation (EGR) valve pintle position input to ensure that the valve responds properly to commands from the PCM. The linear EGR valve is controlled by using an ignition positive driver and ground circuit within the PCM. The driver has the ability to detect an electrical malfunction in the ignition positive or ground circuit. If an electrical malfunction occurs, the driver signals the PCM to set this DTC.

1. 6 - This step tests if voltage is constantly being applied to the EGR valve.

The Powertrain Control Module (PCM) monitors the Exhaust Gas Recirculation (EGR) valve pintle position input to ensure that the valve responds properly to commands from the PCM. The PCM compares the EGR position sensor with desired EGR position when the valve is commanded open. If the difference between the EGR position sensor and Desired EGR Position is more than 15 percent, this DTC will set.

The Exhaust Gas Recirculation (EGR) valve position sensor is monitored by the Powertrain Control Module (PCM). The 5-volt reference circuit, low reference circuit and the EGR valve position signal circuit are used by the PCM to determine the EGR valve position. If EGR valve position sensor signal voltage is pulled below a calibrated value, DTC P0405 sets.

The number below refers to the step number on the diagnostic procedures.

1. 9 - By disconnecting each component one at a time, the component that is pulling the 5-volt reference circuit low will be revealed.

To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx), a Three-Way Catalytic (TWC) converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting the NOx to nitrogen. The TWC also has the ability to store excess oxygen and release the stored oxygen to promote these reactions. This Oxygen Storage Capacity (OSC) is a measurement of the catalysts ability to control emissions. The Powertrain Control Module (PCM) monitors this process using a Heated Oxygen Sensor (HO2S) located in the exhaust stream past the TWC. When the catalyst is functioning properly, the HO2S 2 is slow to respond to a large change in the HO2S 1 signal. When the HO2S 2 responds quickly to a large change in the HO2S 1 signal, the OSC and efficiency of the catalyst is considered to be bad and the Malfunction Indicator Light (MIL) will be illuminated if subsequent tests also indicate a failure.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - If any component DTCs are set, diagnose those DTCs first. A fault in a component can cause the TWC to appear degraded or may have caused its failure.
2. 3 - Clearing the DTCs allows the catalyst test to be completed up to 6 times this ignition cycle. If the A/C is not turned OFF, the diagnostic may not run. The engine must be warmed-up. The TWC needs to be warmed-up by raising the engine speed above idle for the specified time prior to each attempted test. Inspect and see if the DTC passed or failed this ignition cycle. If the DTC does not pass or fail, look for a possible reason that would cause the test to abort.
3. 4 - This step includes tests for conditions that can cause the TWC to appear degraded. Repair any problems found before proceeding.
4. 9 - If the TWC needs to be replaced, make sure that another condition is not present which could damage the TWC. These conditions may include misfire, high engine oil or coolant consumption, retarded spark timing, weak spark, or a rich or lean fuel system. Correct any possible causes of TWC damage before replacing the TWC.

The control module tests the Evaporative (EVAP) emission system for a large leak. The control module monitors the Fuel Tank Pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the control module commands the EVAP canister purge valve OPEN and the EVAP vent valve CLOSED. This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the control module commands the EVAP canister purge valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, this DTC sets. The EVAP valve command table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent valves. See EVAP VALVE COMMAND table.

EVAP VALVE COMMAND

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - This step verifies that a failure condition is active.
2. 4 - Introducing smoke in 15 second intervals may allow smaller leak areas to be more noticeable. When the system is less pressurized, the smoke will sometimes escape in a more condensed manner.
3. 6 - This step verifies proper operation of the Fuel Tank Pressure (FTP) sensor.
4. 7 - A normal operating FTP sensor should increase to more than 5 in. H2O and stop between 6 in. H2O and 7 in. H2O. This step verifies proper operation of the FTP sensor.
5. 9 - This step tests the EVAP purge solenoid vacuum source between the EVAP purge solenoid and intake manifold for restrictions or blockages.

This DTC tests the Evaporative Emission (EVAP) system for a small leak. The control module monitors the Fuel Tank Pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the control module turns the EVAP canister purge valve ON and the EVAP vent valve ON. This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the control module turns the EVAP canister purge valve OFF, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum decay. If the control module detects a leak larger than a calibrated amount, this DTC sets.

The table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP canister purge and vent valves. See EVAP VALVE COMMAND table.

EVAP VALVE COMMAND

The numbers below refer to the step number in the diagnostic procedures.

1. 2 - This step verifies that a failure condition is present.
2. 4 - Introducing smoke in 15 second intervals may allow smaller leak areas to be more noticeable. When system is less pressurized, smoke will sometimes escape in a more condensed manner.
3. 6 - This step verifies that repairs are complete and that there are no other leaks in the system.

An ignition voltage is supplied directly to the Evaporative Emission (EVAP) canister purge valve. The EVAP canister purge valve is Pulse-Width Modulated (PWM). The scan tool displays the amount of ON time as a percentage. The control module monitors the status of the driver. The control module controls the EVAP canister purge valve ON time by grounding the control circuit via an internal switch called a driver. If the control module detects an incorrect voltage for the commanded state of the driver, this DTC sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - This step tests if the concern is active. The EVAP purge valve is PWM. You should hear a clicking sound when the purge valve is commanded to 50 percent. The clicking sound should stop when the EVAP purge valve is commanded to zero percent. The rate at which the valve cycles should increase when the commanded state is increased, and decrease when the commanded state is decreased. Repeat the commands as necessary.
2. 5 - This step verifies that the control module is providing ground to the EVAP purge valve.
3. 6 - This step tests if a ground is constantly being applied to the EVAP purge valve.

This DTC tests the Evaporative (EVAP) emission system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge valve ON and the EVAP canister vent valve ON. This allows a vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge valve OFF and the EVAP canister vent valve OFF. The control module monitors the Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near zero in. H2O in a calibrated time, this DTC sets. The EVAP valve command table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent valves. See EVAP VALVE COMMAND table.

The number below refers to the step numbers in the diagnostic procedures.

1. 4 - This test determines if the failure is present or intermittent.

An ignition voltage is supplied directly to the Evaporative (EVAP) emission canister vent valve. The Powertrain Control Module (PCM) controls the EVAP vent valve by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the controlled component. The PCM monitors the status of the driver. If the PCM detects an incorrect voltage for the commanded state of the driver, DTC P0449 sets.

The table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister vent valve. See EVAP VALVE COMMAND table.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - A click should be heard or felt when the valve operates. Ensure that both the ON and the OFF states are commanded. Repeat the commands as necessary.
2. 5 - This step verifies that the control module is providing ground to the EVAP vent valve.
3. 6 - This step tests if the EVAP vent valve control circuit is grounded.

The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced Evaporative (EVAP) emission diagnostic. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as the fuel tank pressure decreases (negative pressure or vacuum, high voltage). The FTP sensor signal voltage decreases as the fuel tank pressure increases (positive pressure, low voltage). When the FTP sensor signal goes below a predetermined value, DTC P0452 will set.

The table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister vent valve. See EVAP VALVE COMMAND table.

The number below refers to the step number in the diagnostic procedures.

1. 5 - If the FTP sensor voltage is about 5 volts, the FTP sensor signal and the 5-volt reference circuits are okay from the body pass-through connector to the PCM.

The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced Evaporative (EVAP) emission diagnostic. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as the fuel tank pressure decreases (negative pressure or vacuum, high voltage). The FTP sensor signal voltage decreases as the fuel tank pressure increases (positive pressure, low voltage). When the FTP sensor signal voltage goes above a predetermined value, DTC P0453 will set.

The table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister vent valve. See EVAP VALVE COMMAND table.

The number below refers to the step number in the diagnostic procedures.

1. 2 - If DTC P1635 and P1639 are set, the 5-volt reference circuit may be shorted to a voltage.

1. P0480 - Low Speed Cooling Fan Relay Control Circuit
2. P0481 - High Speed Cooling Fan Relay Control Circuit

Battery positive voltage is supplied to the cooling fan 1 relay from the COOL FAN #1 fuse. The Powertrain Control Module (PCM) controls the cooling fan 1 relay by grounding the low speed cooling fan relay control circuit via an internal solid state device called a driver.

Battery positive voltage is supplied to the cooling fan 2 relay and the cooling fan 3 relay from the COOL FAN #2 fuse. The PCM controls the relays by grounding the high speed cooling fan relay control circuit.

When PCM is commanding a relay on, the voltage potential of the control circuit should be low, about zero volts. When the PCM is commanding the control circuit to a relay, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the DTC will set.

PCM will monitor the control circuit for a short to ground, short to voltage, open circuit, open relay coil, or an internally shorted or excessively low resistance relay coil. When PCM detects any of the conditions, DTC will set and the affected driver will be disabled.

The number below refers to the step number in the diagnostic procedures.

1. 2 - Listen for an audible click when the cooling fan 1 relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 3 - Listen for an audible click when the cooling fan 2 and cooling fan 3 relays operate. Command both the ON and OFF states. Repeat the commands as necessary.
3. 4 - Tests for voltage at the coil side of the cooling fan 1 relay. The COOL FAN #1 fuse supplies battery positive voltage to the coil side of the cooling fan 1 relay.

The Vehicle Speed Sensor (VSS) system is a pulse generator consisting of a speed sensor assembly, located in the case extension, and a toothed vehicle speed sensor reluctor wheel, which is pressed onto the final drive carrier assembly. As the vehicle drives forward, the vehicle speed sensor reluctor wheel rotates. This rotation produces a variable AC signal in the pick-up coil that is proportional to vehicle speed. The PCM uses this signal to calculate vehicle speed, shift timing and gear ratios. If the PCM detects a low vehicle speed with a high engine speed while in a drive range, then DTC P0502 sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 - This step tests the ability of the VSS to produce an AC voltage. This step also verifies the integrity of the wiring to the PCM.
2. 4 - This step test the VSS circuit for correct resistance.

The Vehicle Speed Sensor (VSS) system is a pulse generator consisting of a speed sensor assembly, located in the case extension, and a toothed vehicle speed sensor reluctor wheel, which is pressed onto the final drive carrier assembly. As the vehicle drives forward, the vehicle speed sensor reluctor wheel rotates. This rotation produces a variable AC signal in the pick-up coil that is proportional to vehicle speed. The PCM uses this signal to calculate vehicle speed, shift timing and gear ratios. If the PCM detects a large change in vehicle speed in a short period of time, then DTC P0503 sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 - This step tests the ability of the VSS to produce an AC voltage. This step also verifies the integrity of the wiring to the PCM.
2. 4 - This step test the VSS circuit for correct resistance.

The engine idle speed is controlled by the Idle Air Control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The valve consists of a movable pintle, driven by a gear attached to a 2 phase bi-polar permanent magnet electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is fed by 2 circuits from the Powertrain Control Module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key is turned OFF. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If engine idle speed is out of range for a calibrated period of time, an idle speed DTC may set.

The number below refers to the step number in the diagnostic procedures.

1. 5 - This test will determine the ability of the engine controller and IAC valve circuits to control the IAC valve.
2. 7 - This test will determine the ability of the PCM to provide the IAC circuits with a ground. On a normal operating system, the test light should not flash while the IAC counts are incrementing.

The engine idle speed is controlled by the Idle Air Control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The valve consists of a movable pintle, driven by a gear attached to a 2-phase bi-polar permanent magnet electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is fed by 2 circuits from the Powertrain Control Module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition is turned off. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a calibrated period of time, an idle speed DTC may set.

The number below refers to the step number in the diagnostic procedures.

1. 5 - This test will determine the ability of the engine controller and IAC valve circuits to control the IAC valve.
2. 7 - This test will determine the ability of the PCM to provide the IAC valve circuits with a ground. On a normally operating system, the test light should not flash while the IAC counts are incrementing.

PCM monitors the system voltage to make sure that the voltage stays within the proper range. Damage to components, and incorrect data input can occur when the voltage is out of range. The PCM monitors system voltage over an extended length of time. If PCM detects a system voltage outside an expected range for the calibrated length of time, DTC P0560 will set.

This diagnostic applies to internal microprocessor integrity conditions within the Powertrain Control Module (PCM). This diagnostic also addresses if the PCM is not programmed.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 - A DTC P0602 indicates the PCM is not programmed.

The Malfunction Indicator Light (MIL) is located on the Instrument Panel Cluster (IPC). The MIL informs the driver that an emission system fault has occurred and that the engine control system requires service. The control module monitors the MIL control circuit for conditions that are incorrect for the commanded state of the MIL. For example, a failure condition exists if the control module detects low voltage when the MIL is commanded OFF, or high voltage when the MIL is commanded ON. If the control module detects an improper voltage on the MIL control circuit, DTC P0650 will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 5 - This step tests for a short to ground in the MIL control circuit. With the PCM disconnected and ignition on, the MIL should be OFF.
2. 6 - This step tests for a short to voltage on the MIL control circuit. With the fuse removed, there should be no voltage on the MIL control circuit.

The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure which gives an indication of the engine load. The MAP sensor has a 5-volt reference circuit, and a signal circuit. The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit, and provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. With low MAP such as during idle or deceleration, the PCM should detect a low MAP sensor signal voltage. With high MAP such as ignition ON, with the engine OFF or WOT, the PCM should detect a high MAP sensor signal voltage. Certain vehicle models will also use the MAP sensor in order to calculate the Barometric (BARO) pressure when the ignition is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is intermittently high, DTC P1106 will set.

The number below refers to the step number in the diagnostic procedures.

1. 4 - Many intermittent open or shorted circuits occur with harness/connector movement caused by vibration, by engine torque, and by bumps. This step attempts to recreate this condition.

The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure which gives an indication of the engine load. The MAP sensor has a 5-volt reference circuit, and a signal circuit. The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit, and provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. With low MAP such as during idle or deceleration, the PCM should detect a low MAP sensor signal voltage. With high MAP such as ignition on, with engine off or Wide-Open Throttle (WOT), the PCM should detect a high MAP sensor signal voltage. Certain vehicle models will also use the MAP sensor in order to calculate the Barometric (BARO) pressure when the ignition is on, with engine off. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP signal voltage that is intermittently low, DTC P1107 will set.

The number below refers to the step number in the diagnostic procedures.

1. 3 - Many intermittent open or shorted circuits come and go with harness/connector movement caused by vibration, by engine torque, and by bumps. This step attempts to recreate this condition.

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an intermittent high IAT signal voltage, indicating a low temperature, DTC P1111 sets.

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an intermittent low IAT signal voltage, indicating a high temperature, DTC P1112 sets.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P1114 sets.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively high signal voltage, which is a low temperature indication, DTC P1115 sets.

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) in order to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

Rotation of the TP sensor rotor from the closed throttle position to the Wide-Open Throttle (WOT) position provides the PCM with a signal voltage from less than 1.0 volt to more than 4 volts through the signal circuit. If the PCM detects an intermittent and excessively high signal voltage, this DTC will set.

The number below refers to the step number in the diagnostic procedure.

1. 7 - This test will determine an intermittent faulty TP sensor utilizing the DVOM's MIN MAX, 100-millisecond capture mode.

The Throttle Position (TP) sensor is used by the PCM in order to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

Rotation of the TP sensor rotor from the closed throttle position to the Wide-Open Throttle (WOT) position provides the PCM with a signal voltage from less than one volt to more than 4 volts through the TP sensor signal circuit. If PCM detects an intermittent excessively low signal voltage, this DTC will set.

The number below refers to the step number in the diagnostic procedure

1. 6 - This test will determine an intermittent faulty TP sensor utilizing the DVOM's MIN MAX, 100-millisecond capture mode.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. This DTC will set if the HO2S 1 voltage did not switch enough times during a calibrated time period. Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control. Low reference loop.
5. Low reference loop.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference or bias voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The PCM calculates a transition time ratio rich-to-lean and lean-to-rich HO2S voltage transitions. If the calculated transition time ratio is incorrect this DTC will set. Each HO2S 1 has the following circuits

1. HO2S 1 high signal.
2. HO2S 1 low reference.
3. HO2S 1 heater ignition voltage.
4. HO2S 1 heater low control.
5. Low reference loop.

The Crankshaft Position (CKP) system variation learn feature is used to calculate reference period errors caused by slight tolerance variations in the crankshaft, and the CKP sensors. The calculated error allows the Powertrain Control Module (PCM) to accurately compensate for reference period variations. This enhances the ability of the PCM to detect misfire events over a wider range of engine speed and load. The PCM stores the CKP system variation values after a learn procedure has been performed. If the CKP system variation values are not stored in the PCM memory, DTC P1336 sets.

The Ignition Control (IC) module has independent power and ground circuits. The circuits between the IC module and the Powertrain Control Module (PCM) consist of the following circuits

1. IC timing signal.
2. IC timing control.
3. The low-resolution engine speed signal.
4. A low reference.

The IC module sends 3X signals to the PCM. The IC module controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions

1. PCM receives the second 3X signal.
2. PCM applies 5 volts to the IC timing signal circuit.
3. The timing advance switches to PCM control.

The Ignition Control (IC) module has independent power and ground circuits. The circuits between the IC module and the Powertrain Control Module (PCM) consist of the following circuits

1. IC timing signal.
2. IC timing control.
3. The low-resolution engine speed signal.
4. A low reference.

The IC module sends 3X signals to the PCM. The IC module controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions

1. PCM receives the second 3X signal.
2. PCM applies 5 volts to the IC timing signal circuit.
3. The timing advance switches to PCM control.

The Ignition Control (IC) module has independent power and ground circuits. The circuits between the IC module and the Powertrain Control Module (PCM) consist of the following circuits

1. IC timing signal.
2. IC timing control.
3. The low-resolution engine speed signal.
4. A low reference.

The IC module sends 3X signals to the PCM. The IC module controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions

1. PCM receives the second 3X signal.
2. PCM applies 5 volts to the IC timing signal circuit.
3. The timing advance switches to PCM control.
4. If PCM does not monitor IC pulses while IC mode spark advance is commanded DTC P1361 sets.

The number below refers to the step number in the diagnostic procedures.

1. 3 - This step determines if DTC P1362 is also set.

The Ignition Control (IC) module has independent power and ground circuits. The circuits between the IC module and the Powertrain Control Module (PCM) consist of the following circuits

1. IC timing signal.
2. IC timing control.
3. The low-resolution engine speed signal.
4. A low reference.

The IC module sends 3X signals to the PCM. The IC module controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions

1. PCM receives the second 3X signal.
2. PCM applies 5 volts to the IC timing signal circuit.
3. The timing advance switches to PCM control.

The number below refers to the step number in the diagnostic procedures.

1. 3 - This step determines if DTC P1361 has set.

A 3X reference signal is produced by the Ignition Control (IC) module. The IC module calculates the 3X reference signal by dividing the Crankshaft Position (CKP) sensor 7X pulses by 2 when engine is running and CKP synchronizing pulses are being received. The Powertrain Control Module (PCM) uses the 3X reference signal to calculate the engine RPM and CKP at engine speeds greater than 1600 RPM. The PCM also uses these pulses to initiate injector pulses. The PCM compares the 3X reference pulses to the 24X CKP pulses and the Camshaft Position (CMP) pulses. The engine will continue to start and run using only the 24X CKP and CMP sensor signals. If the PCM detects an incorrect number of pulses on the low resolution engine speed signal circuit, DTC P1374 sets.

The Powertrain Control Module (PCM) receives rough road information from the Electronic Brake Control Module (EBCM)/Electronic Brake and Traction Control Module (EBTCM) on the serial data circuit. The PCM uses the rough road information to enhance the misfire diagnostic by distinguishing crankshaft speed variations caused by driving on rough road surfaces from variations caused by true misfires. The EBCM/EBTCM transmits rough road information based on inputs from the wheel speed sensors. If the EBCM/EBTCM detects a condition which will not allow rough road situations to be properly identified while a misfire condition is being detected by the PCM, DTC P1380 will be set.

The Powertrain Control Module (PCM) uses the rough road information to enhance the misfire diagnostic by distinguishing crankshaft speed variations caused by driving on rough road surfaces from variations caused by true misfires. The Electronic Brake Control Module (EBCM)/Electronic Brake and Traction Control Module (EBTCM) transmits rough road information based on inputs from the wheel speed sensors. If a loss of communication occurs which causes the PCM not to receive rough road information while DTC P0300 is requesting the Malfunction Indicator Light (MIL), DTC P1381 will set.

The number below refers to the step number in the diagnostic procedures.

1. 1 - This step will diagnose a malfunction in the serial data circuits.

The Exhaust Gas Recirculation (EGR) valve position sensor is monitored by the Powertrain Control Module (PCM). The 5-volt reference circuit, low reference circuit and EGR valve position signal circuit are used by the PCM to determine the EGR valve position. When ignition is turned on, PCM records the EGR Learned Minimum Position. The PCM compares the EGR Learned Minimum Position parameter to the EGR Position Sensor parameter. If PCM detects that the EGR valve is still open when the PCM is commanding the EGR valve closed, DTC P1404 sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 - This step verifies that the malfunction is present.

This Diagnostic Trouble Code (DTC) tests for undesired intake manifold vacuum flow to the Evaporative (EVAP) emission system. The Powertrain Control Module (PCM) seals the EVAP system by commanding the EVAP purge valve OFF (closed) and the EVAP vent valve ON (closed). The PCM monitors the Fuel Tank Pressure (FTP) sensor to determine if a vacuum is being drawn on the EVAP system. If the vacuum in the EVAP system is more than a calibrated value within a calibrated time, DTC P1441 will set.

The PCM uses the 5-volt reference 1 circuit as a sensor feed to the following sensors

1. TP sensor.
2. MAP sensor.
3. EGR valve pintle position sensor.
4. Fuel Tank Pressure (FTP) sensor.

These 5-volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore, a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. If PCM detects that the voltage is out of tolerance, DTC P1635 sets.

The number below refers to the step number in the diagnostic procedures.

1. 12 - This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

PCM uses the 5-volt reference 2 circuit as a sensor feed for the A/C refrigerant pressure sensor. The PCM monitors the voltage on the 5-volt reference 2 circuit. If voltage is out of tolerance, DTC P1639 will set.

Output Driver Modules (ODM) are chips that are inside the Powertrain Control Module (PCM). ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to the PCM microprocessor. ODM 1 determines if the voltage or the current may cause damage to the PCM. The PCM monitors voltage through the Ignition 1 input. Any incorrect current that is on a circuit to the ODM will cause the ODM to report this DTC.

Output Driver Modules (ODM) are chips that are inside the Powertrain Control Module (PCM). ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to the PCM microprocessor. ODM 2 determines if the voltage or the current may cause damage to the PCM. The PCM monitors voltage through the battery input. Any incorrect current that is on a circuit to the ODM will cause the ODM to report this DTC.

Output Driver Modules (ODM) are chips that are inside the Powertrain Control Module (PCM). ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to the PCM microprocessor. ODM 3 determines if the voltage or the current may cause damage to the PCM. The PCM monitors voltage through the Ignition 1 input. Any incorrect current that is on a circuit to the ODM will cause the ODM to report this DTC.

Output Driver Modules (ODM) are chips that are inside the Powertrain Control Module (PCM). ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to the PCM microprocessor. ODM 4 determines if the voltage or the current may cause damage to the PCM. The PCM monitors voltage through the Ignition 1 input. Any incorrect current that is on a circuit to the ODM will cause the ODM to report this DTC.

See also:
• SENSOR OPERATING RANGE CHARTS - TRUCKS